Principle of Heat Pump
The operating principle of a
heat pump is based on the physical property that the boiling point of a fluid
increases with pressure. By lowering pressure, a medium can be evaporated at
low temperatures while an increase of pressure will lead to a high boiling
point.
This device consists of two heat exchangers, a
compressor and an expansion device. A liquid or a mixture of liquid and vapor
of a pure chemical species flows through an evaporator, where it absorbs heat
at low temperature and, in doing so, is completely vaporized.
The low temperature vapor is compressed by a compressor, which requires external work. The work done on the vapor raises its pressure and temperature to a level where its energy becomes available for use. The vapor flows through a condenser where it gives up its energy as it condenses to a liquid. The liquid is then expanded through an expansion valve back to the evaporator where the cycle repeats. The heat pump was developed as a space heating system where low temperature energy from the ambient air, water, or earth is raised to heating system temperatures by doing compression work with an electric motor-driven compressor.
The low temperature vapor is compressed by a compressor, which requires external work. The work done on the vapor raises its pressure and temperature to a level where its energy becomes available for use. The vapor flows through a condenser where it gives up its energy as it condenses to a liquid. The liquid is then expanded through an expansion valve back to the evaporator where the cycle repeats. The heat pump was developed as a space heating system where low temperature energy from the ambient air, water, or earth is raised to heating system temperatures by doing compression work with an electric motor-driven compressor.
Among the different types of heat
pumps that have been developed, the mechanical heat pump is the most widely
used. Its operating principle is based on compression and expansion of a
working fluid, or so called 'refrigerant'. The refrigerant is the working fluid
that passes through all these components. In the evaporator heat is extracted
from a waste heat source. In the condenser this heat is delivered to the
consumer at a higher temperature level. Electric energy is required to drive
the compressor and this energy is added to the heat that is available in the
condenser. The efficiency of the heat pump is denoted by its COP-Coefficient of
performance, defined as the ratio of total heat delivered by the heat pump to
the amount of electricity needed to drive the heat pump.
The heat pumps have the ability to
upgrade heat to a value more than twice that of the energy consumed by the
device. The potential for application of heat pump is growing and number of
industries have been benefited by recovering low grade waste heat by upgrading
it and using it in the main process stream.
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